This invention relates to a process for the preparation of polyisocyanate addition products suitable as mold release agents.
In the production of molded plastics formed inside the mold (for example, polyurethane-based molded foams having an integral density distribution) it is necessary to either coat the internal walls of the mold with an external mold release agent or to introduce an internal mold release agent into the reaction mixtures so that the molded articles may be easily removed from the mold and faithfully reproduce the internal shape and structure of the mold. The production of integral foams using such internal mold release agents has been described, for example, in British Pat. Nos. 1,365,215 and 1,420,293; U.S. Pat. Nos. 3,726,952; 4,033,912; 4,024,090; 4,058,492 and 4,098,371; and German Offenlegungsschriften 2,319,648; 2,427,273 and 3,012,126.
When external mold release agents are used, the molded products must be carefully freed from mold release agent if they are to be lacquered so that the lacquer coat will adhere firmly. Even when using the mold release agents disclosed in the literature cited above, after-treatment of the molded products is often necessary prior to lacquering.
Lacquered molded plastic articles may also be produced by coating the internal walls of the mold with an "in-mold coating lacquer" before the mold is charged ("in-mold coating process"). For this process, however, it has been necessary to spray the internal walls of the mold with an external mold release agent prior to lacquering to ensure complete removal of the lacquer coated article from its mold. The disadvantage of this process is that the internal walls of the mold must be sprayed with mold release agent before each molding operation.